Method for making microstructured tools having discontinuous topographies, and articles produced therefrom

ABSTRACT

Methods for making a microstructured tool having interspersed topographies are disclosed, and the production of articles therefrom. The article has a major surface including first microstructural features and second microstructural features arranged in a pattern visible at least when viewed normal to the first major surface. The first and second microstructural features are different relative to each other, and are selected from the group consisting of cones, diffraction gratings, lenticulars, segments of a sphere, pyramids, cylinders, fresnels, and prisms.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No.14/117,911, filed Nov. 15, 2013, which is a national stage filing under35 U.S.C. 371 of PCT/US2012/039102, filed May 23, 2012, which claimspriority to U.S. Provisional Patent Application No. 61/491,575, filedMay 31, 2011, the disclosures of which are incorporated by reference intheir entirety herein.

BACKGROUND

Microstructured composite films are produced using metal molding toolsof exacting dimensions that can be time consuming and expensive to make.Many methods for using a patterned tool to replicate a complementarypattern in the surface of a film are well known. However, in manyinstances the pattern resulting from the replication method may belimited by the tool (e.g., certain pattern configurations do not lendthemselves to being replicated by conventional replication methods).Many times there is a need to produce films that bear alphanumerics,security marks, light modulating features, or customized decorativepatterns.

SUMMARY

What is needed is a method, preferably that is relatively rapid andrelatively low-cost, for creating a variety of differentially patterncured microstructured articles without permanent physical modificationof a microreplication tool.

In one aspect, methods described herein include making a molding tool,by coating a radiation curable resin on the first microstructuredsurface of the molding tool, exposing the radiation curable resin to apatterned irradiation, and then removing non-irradiated radiationcurable resin from the molding tool to provide a modifiedmicrostructured surface on the molding tool. Methods are also disclosedherein for introducing at least one region of a second microstructuredsurface to the first microstructured surface of the first molding tool,by contacting a second molding tool having a second microstructuredsurface (which is typically coated with a release agent) against aradiation curable resin coated on the first microstructured surface ofthe first molding tool prior to the patterned irradiation, performingthe patterned irradiation and subsequently removing the second moldingtool and the radiation curable resin from at least one non-irradiatedregion of the modified first molding tool. In some embodiments, theradiation curable material is selected to be sufficiently durable, afterirradiation, to withstand molding processes as part of the modifiedfirst molding tool, while also being removable (e.g., by physical orchemical treatment), to restore the modified first molding tool to itsunmodified condition. The modified first molding tool can optionally betreated to make the modification more permanent, using methods known tothose in the art (e.g., by depositing a metal layer on the modifiedmicrostructured surface). The modified first molding tool can be used asa molding tool in at least some embodiments of methods described hereinfor making differentially pattern cured microstructured articles.

In some embodiments, the present disclosure describes a method of makinga molding tool, the method comprising providing a first molding toolhaving a first microstructured surface that includes a first pluralityof cavities; providing a second molding tool having a secondmicrostructured surface that includes a second plurality of cavities;filling at least one of the first or second pluralities of cavities witha radiation curable resin; contacting the first and second molding toolsagainst the radiation curable resin such that the first and secondpluralities of cavities face each other with a layer of the radiationcurable resin therebetween and in contact with the first and secondpluralities of cavities; exposing the layer of the radiation curableresin to a patterned irradiation through at least one of the firstmolding tool or the second molding tool to provide a correspondingpartially cured resin layer comprising at least one first region and atleast one second region, wherein the at least one first region isirradiated by the patterned irradiation and the at least one secondregion is not irradiated by the patterned irradiation, and wherein atleast one of the first molding tool or the second molding tool istransparent to the patterned irradiation; separating the second moldingtool from the partially cured resin; and separating the non-irradiatedregions of the partially cured resin from the first molding tool, toprovide a molding tool having a microstructured surface that includes apattern of a matrix of first microstructural features and at least onediscontinuous region of second microstructural features.

In another aspect, the present disclosure describes an article having afirst major surface comprising first microstructural features within amatrix of second microstructural features, wherein the firstmicrostructural features are discontinuous, wherein collectively thefirst and second microstructural features form a pattern visible atleast when viewed normal to the first major surface, and wherein thefirst and second microstructural features are independently selectedfrom the group consisting of cones, diffraction gratings, lenticulars,segments of a sphere, pyramids, cylinders, fresnels, and prisms.

In another aspect, the present disclosure describes an article having afirst major surface comprising first microstructural features and secondmicrostructural features arranged in a pattern visible at least whenviewed normal to the first major surface, wherein the first and secondmicrostructural features are different relative to each other, and areselected from the group consisting of cones, diffraction gratings,lenticulars, segments of a sphere, pyramids, cylinders, fresnels, andprisms.

“Cured” in reference to polymers refers to polymers made bycross-linking liquid, flowable or formable monomeric or oligomericprecursors by application of an appropriate energy source to produce asolid material by various means including free-radical polymerization,cationic polymerization, and anionic polymerization.

“Cured oligomeric resin” refers to polymeric materials made by curingcertain curable compositions comprising prepolymeric materials having atleast two repeating monomeric units which may be mixed with othermonomeric materials;

“Differentially pattern cured” refers to the pattern of curing in aradiation curable material upon exposure to a patterned irradiation,wherein different levels of curing occur to form a visible pattern inthe radiation curable material.

“Opaque” refers to a mask that substantially absorbs or reflects a givenirradiation (i.e., at least 90% of the given irradiation is absorbed orreflected, typically at least 95% of the given irradiation is absorbedor reflected).

“Partially cured” refers to part of a radiation curable resin beingcured to such a degree that it will not substantially flow.

“Pattern” refers to a spatially varying appearance. The term “pattern”is at least one of a uniform or periodic pattern, a varying pattern, ora random pattern.

“Patterned irradiation” refers to at least one of irradiating throughtransparent regions of a mask, guiding a beam of light, guiding a beamof electrons, or projecting a digital image.

“Security mark” refers to an element on or in an article of the presentdisclosure that is surrounded by a background appearance. In manyembodiments the security mark is an “island” feature surrounded by acontinuous background appearance. The security mark can changeappearance to a viewer as the viewer changes their point of view of thesecurity mark.

“Visible” refers to being apparent and identifiable (i.e., to ascertaindefinitive characteristics of) to the unaided human eye of normal (i.e.,20/20) vision. By “unaided”, it is meant without the use of a microscopeor magnifying glass.

Many combinations of molding tools, patterned irradiation techniques,and radiation curable materials are included in the methods describedherein. Using these methods, a wide variety of differentially patterncured microstructured articles can be produced without requiring costlymodification of a molding tool.

Exemplary uses of the methods described herein include the production ofarticles having a product security mark, a logo, a trademark, adecorative appearance, and light management properties (e.g., fortransmitted light, reflected light, or retroreflected light).

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 to 4A illustrate steps in an exemplary method of presentdisclosure for making a molding tool;

FIG. 4B illustrates an exemplary embodiment of an exemplary molding toolof the present disclosure;

FIG. 4C illustrates an exemplary embodiment of an article 410 includingelements 420, 435, 482 and 476 of the present disclosure;

FIGS. 5 and 6 illustrate steps in an exemplary method of presentdisclosure for making a molding tool;

FIG. 7 illustrates an exemplary embodiment of an exemplary molding toolof the present disclosure;

FIG. 8 is a digital photographic image of an exemplary embodiment of anarticle of the present disclosure, under ambient lighting conditions;

FIGS. 9A and 9B are digital photographic images of an exemplaryembodiment of an article of the present disclosure, under ambientlighting and retroreflective lighting conditions, respectively;

FIGS. 10A and 10B are digital photographic images of an exemplaryembodiment of an article of the present disclosure, under ambientlighting and retroreflective lighting conditions, respectively;

FIG. 11A is a digital photographic image of an exemplary article of thepresent disclosure, and

FIGS. 11B and 11C are digital photographic images of portions of theexemplary article in FIG. 11A at magnifications of 100× and 200×,respectively;

FIG. 12A is a digital photographic images of a diffraction patterngenerated by directing a beam of a red laser pointer through the largergrooves of the exemplary article shown in FIGS. 11A to 11C, and FIG. 12Bis a digital photographic images of a diffraction pattern generated bydirecting a beam of a red laser pointer through a combination of thelarger grooves and smaller grooves of the exemplary article shown inFIGS. 11A to 11C;

FIG. 13A is a digital photographic images of an exemplary article of thepresent disclosure, and FIGS. 13B and 13C are digital photographicimages of portions of the exemplary article in FIG. 13A at amagnification of 400×;

FIG. 14 is a digital photographic images of an exemplary article of thepresent disclosure; and

FIGS. 15A and 15B are digital photographic images of an exemplaryembodiment of an article of the present disclosure, under ambientlighting and retroreflective lighting conditions, respectively.

Like reference numbers in the various figures indicate like elements.However, it will be understood that the use of a number to refer to acomponent in a given figure is not intended to limit the component inanother figure labeled with the same number. Some elements may bepresent in identical or equivalent multiples; in such cases only one ormore representative elements may be designated by a reference number butit will be understood that such reference numbers apply to all suchidentical elements. Unless otherwise indicated, all figures and drawingsin this document are not to scale and are chosen for the purpose ofillustrating different exemplary embodiments of the description. Inparticular the dimensions of the various components are depicted inillustrative terms only, and no relationship between the dimensions ofthe various components should be inferred from the drawings, unless soindicated. Although terms such as “top”, bottom”, “upper”, lower”,“under”, “over”, “front”, “back”, “outward”, “inward”, “up” and “down”,and “first” and “second” may be used in this disclosure, it should beunderstood that those terms are used in their relative sense only unlessotherwise noted. In particular, in some embodiments certain componentsmay be present in interchangeable and/or identical multiples (e.g.,pairs). For these components, the designation of “first” and “second”may apply to the order of use, as noted herein (with it being irrelevantas to which one of the components is selected to be used first).

DETAILED DESCRIPTION

The ability to produce molding tools with microstructures bearingmultiple complex unrelated features at various orientations is notachievable with conventional machining techniques. If such a machiningtechnique did exist in order to achieve any of these desired outcomes, aspecialty tool would need to be fabricated for each outcome.

The present disclosure describes methods to produce patterned articlesbearing interspersed microstructures. In some embodiments, the patternedarticles are characterized by having patterns of microstructurescomprising one topography surrounded by microstructures of at least onedifferent topography. In some embodiments, the patterned articles havepatterns of microstructures comprising one topography surrounded bymicrostructures of the same topography in at least one differentorientation.

In some embodiments, a patterned molding tool is produced by coating amolding tool bearing an array of microstructures with a radiationcurable resin; laminating the structured side of a release film bearinga second microstructure to the resin; placing a mask in intimate contactwith the release film; passing radiation through the mask and structuredrelease film to cure the resin; removing the mask and structured releaseliner; removing the uncured resin from the tool with a suitable solvent;and applying a release coating to the patterned molding tool. Thepatterned tool can be used, for example, to produce articles by cast andcure microreplication or replicated by nickel electroforming to producea metallic nickel tool suitable for cast and cure and other alternativemanufacturing processes including compression molding, extrusionembossing, or injection molding.

The term “microstructure”, used herein in the context of an articlehaving a surface bearing microstructure, means the configuration of asurface which depicts or characterizes the predetermined desiredutilitarian purpose or function of said article. Discontinuities, suchas projections and indentations in the surface will deviate in profilefrom the average profile or center line drawn through the microstructuresuch that the sum of the areas embraced by the surface profile above theline is equal to the sum of those areas below the line, said line beingessentially parallel to the nominal surface (bearing the microstructure)of the article. The heights of said deviations will be ±0.005 micrometerto ±750 micrometers through a representative characteristic length ofthe surface (e.g., 1 centimeter to 30 centimeters). Said averageprofile, or center line, can be plano, concave, convex, aspheric, orcombinations thereof. Articles where said deviations are of low order(e.g., from ±0.005 micrometer to ±0.1 micrometer or, preferably, from±0.005 micrometer to ±0.05 micrometers) and said deviations are ofinfrequent or minimal occurrence (i.e., the surface is free of anysignificant discontinuities), are those where the microstructure-bearingsurface is an essentially “flat” or “perfectly smooth” surface, sucharticles being useful, for example, as precision optical elements orelements with a precision optical interface, such as ophthalmic lenses.Articles where said deviations are of said low order and of frequentoccurrence are those, for example, bearing utilitarian discontinuities,as in the case of articles having anti-reflective microstructure.Articles where said deviations are of high order (e.g., from ±0.1micrometer to ±750 micrometer) and attributable to microstructurecomprising a plurality of utilitarian discontinuities which are the sameor different and spaced apart or contiguous in a random or orderedmanner, are articles such as retroreflective cube-corner sheeting,linear Fresnel lenses, and video discs. The microstructure-bearingsurface can contain utilitarian discontinuities of both said low andhigh orders. The microstructure-bearing surface may contain extraneousor non-utilitarian discontinuities so long as the amounts or typesthereof do not significantly interfere with or adversely affect thepredetermined desired utilities of said articles. In some embodiments,microstructural elements include at least one of cones, diffractiongratings, lenticulars, segments of a sphere, pyramids, cylinders,fresnels, or prisms. It may be necessary or desirable to select aparticular oligomeric composition whose shrinkage upon curing does notresult in said interfering extraneous discontinuities (e.g., acomposition which shrinks only 2% to 6%). The profiles and thedimensions and spacing of said discontinuities are those discernible byan electron microscope at 1000× to 100,000×, or an optical microscope at10× to 1000×.

FIG. 1 illustrates an exemplary embodiment of first microstructured tool170 and second microstructured tool 180. First microstructured tool 170includes body portion 176 having opposed first and second major surfaces171, 172. First major surface 171 includes microstructured layer 175,which includes first plurality of cavities 177 and first plurality ofpeaks 178. Second microstructured tool 180 includes body portion 186having first major surface 181 generally opposite second major surface182, and first major surface 181 includes microstructured layer 185,having second plurality of cavities 187 and second plurality of peaks188.

FIG. 2 illustrates first major surface 171 of first microstructured tool170 contacting a radiation curable resin 130. FIG. 3 illustrates firstand second molding tools 170 and 180 contacting against radiationcurable resin 130 such that the first pluralities of cavities 177 andsecond plurality of cavities 188 face each other with layer of theradiation curable resin 130 therebetween and in contact with first andsecond pluralities of cavities 177 and 188.

FIG. 4A illustrates a patterned irradiation of radiation curable resin430 sandwiched between first microstructured tool 490 and secondmicrostructured tool 480, with the same relative configuration ofmicrostructured layers as in FIG. 3. In the configuration shown in FIG.4A, irradiation 440 passes through mask 450 in radiation transparentregions 451, while radiation opaque regions 452 block at least 90% ofradiation 440 incident upon radiation opaque regions 452.

In exemplary embodiments of the method described herein, at least one ofthe first or second molding tools is transparent to the patternedirradiation. Irradiation of a radiation curable resin through atransparent molding tool is described, for example, in U.S. Pat. No.5,435,816 (Spurgeon et al.) and U.S. Pat. No. 5,425,848 (Haisma et al.).In the exemplary embodiment illustrated in FIG. 4A, secondmicrostructured tool 480 is selected to be transparent to irradiation440.

Irradiating 440 passing through radiation transparent regions 451 inmask 450 and then through radiation transparent microstructured tool 480at least partially cures radiation curable resin 430 in first region431, while radiation curable resin 430 in second region 432 does notreceive any more than 10% of radiation 440 incident on radiation opaqueregions 452 in mask 450. Subsequent to the patterned irradiation ofradiation curable resin 430, second microstructured tool 480 isseparated from the at least partially cured radiation curable resin onmicrostructured tool 490, and radiation curable resin from secondregions (i.e., “non-irradiated” regions) is removed, typically bywashing with a suitable solvent (e.g., ethanol, although other solventsmay be useful, depending on the nature of the radiation curable resin).

FIG. 4B illustrates exemplary molding tool 400 made according to amethod of the present description, having a microstructured layer 491that includes plurality of cavities 427 interspersed with plurality ofcavities 437. Molding tool 400 can optionally be treated with a releasecoating to facility the replication of articles from the surface ofmicrostructured layer 491.

It will be noted from the above description that molding tool 400 is amodified version of first molding tool 490, and it should also be notedthat modification of first molding tool 490 to form molding tool 400 didnot require any machining of molding tool 490, and could be carried outwith a wide selection of second molding tools 480 to produce acorrespondingly wide selection of molding tools 400. An additionaladvantage of the present method is that the radiation curable resin canbe selected to be sufficiently durable after radiation curing to permitreplication of molding tool 400, while also being removable undersuitable conditions in order to restore first molding tool 490 to itsoriginal, unmodified condition, thereby enabling a wide selection ofmolding tools 400 to be made (sequentially) from a single molding tool490.

In some exemplary embodiments, first major surface 171 of firststructured tool 170 and first major surface 181 of second structuredtool 180 are sufficiently complementary to permit first plurality ofpeaks 178 to nest within second plurality of cavities 187. FIG. 5illustrates first major surface 171 of first microstructured tool 170contacting a radiation curable resin 130, and FIG. 6 illustrates a firstand second molding tools 170 and 180 each contacting against radiationcurable resin 130 such that first pluralities of cavities 177 and secondplurality of cavities 188 face each other with layer of the radiationcurable resin 130 therebetween. First plurality of peaks 178 is nestedin second plurality of cavities 187, and FIG. 7 illustrates exemplarymolding tool 700 resulting from a patterned irradiation of the radiationcurable resin 130 shown in FIG. 6, followed by removal of second moldingtool 180 and removal of non-irradiated radiation curable resin, which inturn results in having a microstructured layer 791 in exemplary moldingtool 700 that includes plurality of cavities 727 (in non-irradiatedregions 732) interspersed with plurality of cavities 737 (in irradiatedregions 731) defined within cured resin 735.

In exemplary embodiments of the methods described herein that requireirradiation, examples of types of irradiation include electron beam,ultraviolet light, and visible light. Electron beam radiation, which isalso known as ionizing radiation, can be used typically at a dosage in arange from about 0.1 Mrad to about 10 Mrad (more typically in a rangefrom about 1 Mrad to about 10 Mrad. Ultraviolet radiation refers tonon-particulate radiation having a wavelength within the range of about200 to about 400 nanometers (typically within the range of about 250 toabout 400 nanometers). Typically, the ultraviolet radiation can beprovided by ultraviolet lights at a dosage of 50 to 1500millijoules/cm². Visible radiation refers to non-particulate radiationhaving a wavelength within the range of about 400 nanometers to about700 nanometers.

Any suitable patterned irradiation can be used that provides acorrespondingly patterned partially cured resin having at least onefirst region and at least one second region, wherein the at least onefirst region is irradiated by the patterned irradiation and the at leastone second region is not irradiated by the patterned irradiation. “Notirradiated” can include a minor amount of irradiation, but not more than10% (in some embodiments up to 5%, 2%, or even 1%, as well as zero) ofthe level of irradiation to which the at least one first region isexposed.

An example of patterned irradiation of radiation curable resin includesat least one of irradiating through transparent regions of a mask,guiding a beam of light, guiding a beam of electrons, or projecting adigital image. Combinations of these patterned irradiation techniquesmay also be used. Suitable adjustment of power level, irradiation time,and distance from the radiation curable resin may be made to obtain adesired level of curing of the resin.

Embodiments of irradiating through transparent regions of a mask includeusing a mask having at least one transparent region and at least oneopaque region. The transparency and opacity of regions in the mask areselected with respect to the irradiation source(s). For example, in someembodiments, when the irradiation source is visible light, a suitablemask can include a film that is transparent to visible light and havingat least one opaque (to visible light) region printed thereon (e.g., bya laser printer). In some other embodiments, when the irradiation sourceis UV light, a suitable mask can include can include a film that istransparent to visible light and having at least one opaque (to UVlight) region printed thereon. In some other embodiments, where, forexample, electron beam irradiation is used, a suitable mask may includea sheet of aluminum having open (i.e., transparent) regions therein.

In some embodiments, the radiation curable resin is at least partiallycurable by visible light, and a suitable irradiation source provides atleast visible light and is other than a laser light source. Suitableexamples of visible light sources are well known in the art (e.g.,fluorescent lamps).

In some embodiments, the radiation curable resin is at least partiallycurable by UV light, and a suitable irradiation source provides at leastUV light and is other than a laser light source. Suitable irradiationsources that provide UV light are well known in the art, and include,for example, an array of light emitting diode (LED) lamps (includingthose available, for example, from Clearstone Technologies, Minneapolis,Minn., under the trade designation “MODEL LN 120-395B-120”), and in someembodiments the irradiation conditions include irradiating with 395nanometer UV light with an energy output level of about 170 milliwattsper square centimeter.

In some embodiments, the radiation source can be a laser providing abeam of light. The beam of light can be guided relative to the radiationcurable resin (e.g., with mirrors, or by moving the molding tool, orboth) to generate the patterned irradiation. The laser used forirradiating the radiation curable resin may be any suitable laseroperating at a visible and/or ultraviolet output wavelength. Examples ofsuitable lasers include gas lasers, excimer lasers, solid state lasers,and chemical lasers. Exemplary gas lasers include: argon-ion lasers(e.g., those which emit light at 458 nm, 488 nm or 514.5 nm);carbon-monoxide lasers (e.g., those which can produce power of up to 500kW); and metal ion lasers, which are gas lasers that generate deepultraviolet wavelengths (e.g., helium-silver (HeAg) 224 nm lasers andneon-copper (NeCu) 248 nm lasers).

Chemical lasers include excimer lasers, which are powered by a chemicalreaction involving an excited dimer (i.e., an “excimer”) having ashort-lived dimeric or heterodimeric molecule formed from two species(atoms), at least one of which is in an excited electronic state. Theytypically produce ultraviolet light. Commonly used excimer moleculesinclude noble gas compounds (KrCl (222 nm), KrF (248 nm), XeCl (308 nm),and XeF (351 nm)).

Solid state laser materials are commonly made by doping a crystallinesolid host with ions that provide the required energy states. Examplesinclude ruby lasers (e.g., made from ruby or chromium-doped sapphire).Another common type is made from neodymium-doped yttrium aluminum garnet(YAG), known as Nd:YAG. Nd:YAG lasers can produce high powers in theinfrared spectrum at 1064 nm. Nd:YAG lasers are also commonly frequencydoubled to produce 532 nm when a visible (green) coherent source isdesired.

The laser may be used in pulsed and/or continuous wave mode. Forexample, the laser may operate at least partially in continuous wavemode and/or at least partially in pulsed mode.

The laser beam is typically optically directed or scanned and modulatedto achieve the desired irradiation pattern. The laser beam may bedirected through a combination of one or more mirrors (e.g., rotatingmirrors and/or scanning mirrors) and/or lenses. Alternatively or inaddition, the substrate can be moved relative to the laser beam.

In some embodiments, the source of irradiation is a beam of electrons. Asuitable mask (e.g., an aluminum mask) can be used in conjunction withthe beam of electrons to generate a patterned irradiation. An example ofa suitable electron beam (“e-beam”) system is available from EnergySciences Inc., Wilmington, Mass., under the trade designation “MODELCB-300 ELECTRON BEAM SYSTEM”. Alternatively, electron beam lithographycan be used to guide a beam of electrons in a patterned irradiation.Suitable operating conditions can be selected depending on the radiationcurable resin being used. In some embodiments, the electron beam systemcan be operated at 200 kV voltage to deliver a dose of 2-5 megarads toprovide cure to the radiation curable resin.

In some embodiments, methods described herein include irradiation usinga projection of a digital image. Any suitable projection technique toproject irradiation as a digital image may be used. Projection of adigital image may be achieved, for example, using a plane light sourcewith cooperation of a digital micromirror device or liquid crystaldisplay to scan selected zones of the radiation curable resin to cause apatterned irradiation, as has been used in rapid prototyping technology(see, e.g., U.S. Pat. No. 7,079,915 (Huang et al.)).

Compositions curable by UV irradiation generally include at least onephotoinitiator. The photoinitiator can be used at a concentration in arange from 0.1 wt. % to 10 wt. %. More typically, the photoinitiator isused at a concentration in a range from 0.2 wt. % to 3 wt. %.

In general the photoinitiator is at least partially soluble (e.g., atthe processing temperature of the resin) and substantially colorlessafter being polymerized. The photoinitiator may be colored (e.g.,yellow), provided that the photoinitiator is rendered substantiallycolorless after exposure to the UV light source.

Suitable photoinitiators include monoacylphosphine oxide andbisacylphosphine oxide. Available mono or bisacylphosphine oxidephotoinitiators include 2,4,6-trimethylbenzoydiphenylphosphine oxide,available from BASF Corporation, Clifton, N.J., under the tradedesignation “LUCIRIN TPO”, ethyl-2,4,6-trimethylbenzoylphenylphosphinate, also available from BASF Corporation, under the tradedesignation “LUCIRIN TPO-L”, and bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide available from CibaSpecialty Chemicals, Tarrytown, N.Y., under the trade designation“IRGACURE 819”. Other suitable photoinitiators include2-hydroxy-2-methyl-1-phenyl-propan-1-one, available from Ciba SpecialtyChemicals, under the trade designation “DAROCUR 1173”, as well as otherphotoinitiators available from Ciba Specialty Chemicals, under the tradedesignations “DAROCUR 4265”, “IRGACURE 651”, “IRGACURE 1800”, “IRGACURE369”, “IRGACURE 1700”, and “IRGACURE 907”.

Free radical scavengers or antioxidants may be used, typically, in arange from about 0.01 wt. % to 0.5 wt. %. Suitable antioxidants includehindered phenolic resins such as those available from Ciba SpecialtyChemicals, under the trade designations “IRGANOX 1010”, “IRGANOX 1076”,“IRGANOX 1035”, and “IRGAFOS 168”.

Radiation curable resin that forms the articles of the presentdisclosure can be cured in one or more steps. For example, radiationsources (e.g., ultraviolet light, visible light, e-beam) can be selecteddepending on the nature of the radiation curable resin.

Exemplary radiation curable polymeric materials include reactive resinsystems capable of being cross-linked by a free radical polymerizationmechanism by exposure to actinic radiation (e.g., electron beam,ultraviolet light, or visible light). Radiation-initiated cationicallypolymerizable resins also may be used. Reactive resins suitable forforming the array of elements may be blends of photoinitiator and atleast one compound bearing an acrylate group. Preferably, the resinblend contains a monofunctional, a difunctional, or a polyfunctionalcompound to ensure formation of a cross-linked polymeric network uponirradiation.

Illustrative examples of resins that are capable of being polymerized bya free radical mechanism that can be used herein include acrylic-basedresins derived from epoxies, polyesters, polyethers, and urethanes,ethylenically unsaturated compounds, aminoplast derivatives having atleast one pendant acrylate group, isocyanate derivatives having at leastone pendant acrylate group, epoxy resins other than acrylated epoxies,and mixtures and combinations thereof. The term acrylate is used here toencompass both acrylates and methacrylates.

Other illustrative examples of radiation curable resins useful in thepresent description can include polymerizable thiol-ene compositionshaving at least one monomer or oligomer having a plurality offree-radiacally polymerizable ethylenically unsaturated groups, and atleast one compound having a plurality of thiol groups, and an initiator(e.g., those described in U.S. Pat. No. 5,876,805 (Ostlie), thedisclosure of which is incorporated herein by reference).

A molding tool of the current disclosure can include a roll, acontinuous belt, a film, a metal plate, and a glass plate. Forcontinuous production of articles of the current disclosure, the moldingtool is typically a roll or a continuous belt. The molding tool has amicrostructured molding surface having a plurality of cavities openingthereon which have the shape and size suitable for forming desiredelements (e.g., cube-corner elements). The cavities, and thus resultantelements may be, for example cube-corner elements such as three sidedpyramids having one cube-corner each (e.g., such as are disclosed in theU.S. Pat. No. 4,588,258 (Hoopman)) have a rectangular base with tworectangular sides and two triangular sides such that each element hastwo cube-corners each (e.g., such as are disclosed in U.S. Pat. No.4,938,563 (Nelson et al.)), or of other desired shape, having at leastone cube corner each (e.g., such as are disclosed in U.S. Pat. No.4,895,428 (Nelson et al.)). It will be understood by those skilled inthe art that any cube-corner element may be used in accordance with thepresent disclosure. The shape of the tooling cavities, and thusresultant article structures, may also be, for example, curve-sidedprisms, truncated pyramids, lenslets, micro-needles, fasteners, stems,micro-flow channels and a variety of other geometries. The pitch of thesurface refers to the repeat distance from one cavity or structure tothe next adjacent cavity or structure.

In some embodiments of the method described herein, irradiations can beperformed by irradiation through a transparent molding tool, such asdisclosed in U.S. Pat. No. 5,435,816 (Spurgeon et al.).

In some embodiments, it may be desirable to provide an agent thatpromotes adhesion of radiation curable resin to the firstmicrostructured molding tool. In embodiments wherein the firstmicrostructured molding tool has a metal microstructured surface,adhesion promotion agents can include silane coupling agents. Suitablesilane coupling agents include, for example,gamma-methacryloxypropyltrimethoxysilane, vinyltriethoxysilane,tris(2-methoxyethoxy)vinylsilane,3,4-epoxycyclohexylmethyltrimethoxysilane,gamma-glycidoxypropyltrimethoxysilane, andgamma-mercaptopropyltrimethoxysilane (e.g., as respectively available asA-174, A-151, A-172, A-186, A-187, and A-189 from Dow Chemical Co.);allyltriethoxysilane, diallyldichlorosilane, divinyldiethoxysilane, andm,p-styrylethyltrimethoxysilane (e.g., as commercially availablerespectively as A0564, D4050, D6205, and S1588 from United ChemicalIndustries, Bristol, Pa.); 3-(2-aminoethylamino)propyltrimethoxysilane;vinyltriacetoxysilane; methyltriethoxysilane; and similar compounds; andmixtures thereof. Other agents that facilitate increased adhesion ofradiation curable resin to the microstructures surface of the firstmicrostructured tool can also be used.

In some embodiment of the method described herein, a differentialpattern curing may be included during the preparation of film articlesfrom molding tools of the present description. Differential patterncuring can be accomplished by methods described herein, as well as thosedescribed in U.S. Patent Application No. 61/491,616, entitled “METHODSFOR MAKING DIFFERENTIALLY PATTERN CURED MICROSTRUCTURED ARTICLES”, filedon the same date as the instant application, the disclosure of which isincorporated herein by reference.

In some embodiments, articles of the present description include a firstmajor surface comprising first microstructural features within a matrixof second microstructural features, wherein the first major surface issupported on a land layer, and the land layer and first major surfacecomprise a monolithic structure. In some other embodiments, articles ofthe present description include a first major surface comprising firstmicrostructural features within a matrix of second microstructuralfeatures, wherein the first major surface is supported on an overlayfilm, and may or may not include a land layer having a thickness in arange of greater than 0 micrometer up to 150 micrometers.

In some embodiments, articles of the present description include anoverlay film. The overlay film can be any conventional film used forsuch purpose, including ionomeric ethylene copolymers, plasticized vinylhalide polymers, acid-functional ethylene copolymers, aliphaticpolyurethanes, aromatic polyurethanes, other radiation transmissiveelastomers, and combinations thereof. In some embodiments, the overlayfilm may be a light transmissive support layer.

The light transmissive support layer typically comprises a low elasticmodulus polymer to impart easy bending, curling, flexing, conforming, orstretching to the resultant retroreflective composite. Generally, thelight transmissive support layer comprises a polymeric film having anelastic modulus of less than 13×10⁸ pascals, and a glass transitiontemperature less than about 50° C. The polymer preferably is such thatthe light transmissive support layer retains its physical integrityunder the conditions it is exposed to as the resultant compositeretroreflective sheeting is formed. The polymer desirably has a Vicatsoftening temperature that is greater than 50° C. The linear moldshrinkage of the polymer desirably is less than 1 percent, althoughcertain combinations of polymeric materials for the cube-corner elementsand the overlay film will tolerate a greater extent of shrinking of theoverlay film. Preferred polymeric materials are resistant to degradationby ultraviolet (“UV”) light radiation so that the retroreflectivesheeting can be used for long-term outdoor applications. The lighttransmissive support layer may be substantially transparent. Forinstance, films with a matte finish that become transparent when theresin composition is applied thereto, or that only become transparentduring the fabrication process (e.g., in response to the curingconditions used to form the array of cube-corner elements) are usefulherein.

The light transmissive support layer may be either a single layer ormulti-layer component as desired. If multilayer, the layer to which thearray of cube-corner elements is secured should have the propertiesdescribed herein as useful in that regard with other layers not incontact with the array of cube-corner elements having selectedcharacteristics as necessary to impart desired characteristics to theresultant composite retroreflective sheeting. Either surface of thelight transmissive support layer may contain printed or formed (e.g.,stamped or embossed) symbols and/or indicia, such as generally describedin U.S. Pat. No. 5,763,049 (Frey et al).

Exemplary polymers that may be employed in the light transmissivesupport layer used herein include fluorinated polymers, ionomericethylene copolymers, low density polyethylenes, plasticized vinyl halidepolymers, and polyethylene copolymers.

Exemplary fluorinated polymers include poly(chlorotrifluoroethylene)(e.g., such as that available from 3M Company, St. Paul, Minn., underthe trade designation “KEL-F800”),poly(tetrafluoroethylene-co-hexafluoropropylene) (e.g., such as thatavailable from Norton Performance, Brampton, Mass., under the tradedesignation “EXAC FEP”),poly(tetrafluoroethylene-co-perfluoro(alkyl)vinylether) (e.g., such asthat available from Norton Performance under the trade designation “EXACPEA”), and poly(vinylidene fluoride-co-hexafluoropropylene) (e.g., suchas that available from Pennwalt Corporation, Philadelphia, Pa., underthe trade designation “KYNAR FLEX-2800”).

Exemplary ionomeric ethylene copolymers includepoly(ethylene-co-methacrylic acid) with sodium or zinc ions (e.g., suchas those available from E.I. duPont Nemours, Wilmington, Del., under thetrade designations “SURLYN-8920” and “SURLYN-9910”).

Exemplary low density polyethylenes include low density polyethylene,linear low density polyethylene, and very low density polyethylene.

Exemplary plasticized vinyl halide polymers include plasticizedpoly(vinychloride).

Exemplary polyethylene copolymers that include acid functional polymersinclude (e.g., poly(ethylene-co-acrylic acid) (EAA),poly(ethylene-co-methacrylic acid) (EMA), poly(ethylene-co-maleic acid),and poly(ethylene-co-fumaric acid)), acrylic functional polymers (e.g.,poly(ethylene-co-alkylacrylates) where the alkyl group is methyl, ethyl,propyl, butyl, et cetera, or CH3(CH2)n- where n is 0 to 12), andpoly(ethylene-co-vinylacetate).

In some embodiments, the light transmissive support layer can includealiphatic and aromatic polyurethanes derived from the following monomers(i)-(iii):

-   -   (i) diisocyanates such as dicyclohexylmethane-4,4′-diisocyanate,        isophorone diisocyanate, 1,6-hexamethylene diisocyanate,        cyclohexyl diisocyanate, diphenylmethane diisocyanate, and        combinations of these diisocyanates;    -   (ii) polydiols such as polypentyleneadipate glycol,        polytetramethylene ether glycol, polycaprolactonediol,        poly-1,2-butylene oxide glycol, and combinations of these        polydiols; and    -   (iii) chain extenders such as butanediol and hexanediol.        Exemplary urethane polymers include those available from Morton        International Inc., Seabrook, N.H., under the trade designations        “PN-04” and “3429”, and the urethane polymer available        from B. F. Goodrich Company, Cleveland, Ohio, under the trade        designation “X-4107”.

The exemplary polymers that may be employed in the light transmissivesupport layer used herein may also be used in combination with eachother. Preferred polymers for the light transmissive support layerinclude: the ethylene copolymers that contain units that containcarboxyl groups or esters of carboxylic acids (e.g.,poly(ethylene-co-acrylic acid) (EAA), poly(ethylene-co-methacrylic acid)(EMA), poly(ethylene-co-vinylacetate)), ionomeric ethylene copolymers,plasticized poly(vinylchloride), and the aliphatic urethanes. Thesepolymers may be preferred, for example, for at least one of thefollowing reasons: suitable mechanical properties, good adhesions to thecomposite cube-corner layer, clarity, and environmental stability.

Depending on the flexibility of the overlay film, the overlay film maybe supported with suitable carrier layer that provides structural andmechanical durability to the overlay element during casting andsolidification or curing. The carrier layer may be stripped from overlayelement after the resulting article is removed from the molding tool, orleft intact for further processing of the resulting article. Use of sucha carrier layer is particularly preferred for low modulus overlay films.The carrier layer can be any conventional films, papers or foils usedfor such purpose, including polyester films, cellulose acetate films,polypropylene films, polycarbonate films, printing paper, kraft paper,security paper, packaging paper, aluminum foil, and copper foil. Whenthe radiation curable resin needs to be irradiated, but the carrierlayer is not transparent to the irradiation, the mold is selected to betransparent to the irradiation and irradiation is directed through themold to the radiation curable resin.

In some embodiments, articles described herein include a reinforcingmaterial. The reinforcing material may include at least one of a wovenmaterial, a nonwoven material, a filament, a yarn, or a wire. Thereinforcing material can be introduced into the resin prior to radiationcuring of the article, using conventional techniques.

In some embodiments, articles of the disclosure have a first majorsurface comprising first microstructural features and secondmicrostructural features arranged in a pattern visible at least whenviewed normal to the first major surface, wherein the first and secondmicrostructural features are different relative to each other, and areselected from the group consisting of cones, diffraction gratings,lenticulars, segments of a sphere, pyramids, cylinders, fresnels,prisms, and combinations thereof. In some embodiments, the firstmicrostructural features have a first pitch, wherein the first pitch isno greater than 1000 micrometers (in some embodiments, no greater than500, 100, 50, 20, 10, 5, 2, 1, 0.5, 0.2, or even no greater than 0.1micrometer). In some embodiments, the second microstructural featureshave a second pitch, wherein the second pitch is no greater than 1000micrometers (in some embodiments, no greater than 500, 100, 50, 20, 10,5, 2, 1, 0.5, 0.2, or even no greater than 0.1 micrometer). In someembodiments, the second pitch is no more than 50% (in some embodiments,no more than 20%, 10%, 5%, 2%, or even no more than 1%) of the firstpitch.

In some embodiments, the article comprises at least one of colorant orpigment. In some embodiments, the article comprises opaque filler.Exemplary colorants and pigments include titanium dioxide, phthalo blue,red iron oxide, various clays, calcium carbonate, mica, silicas, andtalcs. Exemplary fillers include glass beads or fibers, carbon black,flock and mineral reinforcements. Colorants, pigments, and/or fillerscan be incorporated into the articles described herein, for example, byadding them using conventional techniques into the polymeric material.

In some embodiments, the article includes a metalized layer. Methods ofproviding a metalized layer over a cured radiation curable resin arewell known in the art, and include those methods for making metalizedretroreflective sheeting described in U.S. Pat. No. 4,801,193 (Martin).

Any of a variety of patterns of a matrix of first optical elementshaving at least one discontinuous region of second optical elements canbe provided. For example, in some embodiments a discontinuous region maybe in any of a variety of geometric shapes including a circle, oval,square, rectangle, triangle, alphanumeric, etc. In another aspect, forexample, in some embodiments, there is a plurality of discontinuousregions of second optical elements within a matrix of first opticalelements. In some embodiments at least a portion of the matrix and atleast one discontinuous region (and optionally other discontinuousregions if present) collectively exhibit at least a first (second,third, or more) image or indicia (which may be, for example, a trademarkor copyrighted material, including a registered trademark or registeredcopyright as defined under any of the countries, territories, etc. ofthe world (including the United States)). The patterns of the matrix offirst optical elements having at least one discontinuous region ofsecond optical elements (optional additional discontinuous regions) aretypically created by the arrangement of the tool used to create opticalelements in the article and/or the patterned irradiation used in themethod for making the article.

Exemplary uses of the methods described herein include the production ofarticles having a product security mark, a logo, a trademark, adecorative appearance, and light management properties (e.g., fortransmitted light, reflected light, or retroreflected light).

Embodiments

Item 1. A method of making a molding tool, the method comprising:

providing a first molding tool having a first microstructured surfacethat includes a first plurality of cavities;

providing a second molding tool having a second microstructured surfacethat includes a second plurality of cavities;

filling at least one of the first or second pluralities of cavities witha radiation curable resin;

contacting the first and second molding tools against the radiationcurable resin such that the first and second pluralities of cavitiesface each other with a layer of the radiation curable resin therebetweenand in contact with the first and second pluralities of cavities;

exposing the layer of the radiation curable resin to a patternedirradiation through at least one of the first molding tool or the secondmolding tool to provide a corresponding partially cured resin layercomprising at least one first region and at least one second region,wherein the at least one first region is irradiated by the patternedirradiation and the at least one second region is not irradiated by thepatterned irradiation, and wherein at least one of the first moldingtool or the second molding tool is transparent to the patternedirradiation;

separating the second molding tool from the partially cured resin; and

separating the non-irradiated regions of the partially cured resin fromthe first molding tool, to provide a molding tool having amicrostructured surface that includes a pattern of a matrix of firstmicrostructural features and at least one discontinuous region of secondmicrostructural features.

Item 2. The method of item 1, wherein the first molding tool is any oneof a roll, a belt, a film, a metal plate, or a glass plate.

Item 3. The method of item 1 or 2, wherein the patterned irradiationcomprises at least one of irradiating through transparent regions of amask, guiding a beam of light, guiding a beam of electrons, orprojecting a digital image.

Item 4. The method of item 1, wherein the first microstructured surfaceshas a first topography and the second microstructured surfaces has asecond topography, and wherein the first and second topographies arenonidentical with respect to each other.

Item 5. The method of item 4, wherein the first and second topographieseach have an orientation axis and wherein the orientation axes arenonaligned with respect to each other while exposing the resin layer tothe patterned irradiation.

Item 6. The method of item 1, wherein the first microstructured surfaceshas a first topography and the second microstructured surfaces has asecond topography, and wherein the first and second topographies areidentical with respect to each other.

Item 7. The method of item 6, wherein the first and second topographieseach have an orientation axis and wherein the orientation axes arenonaligned with respect to each other while exposing the resin layer tothe patterned irradiation.

Item 8. The method of any preceding item, wherein the secondmicrostructured surface comprises a release agent.

Item 9. The method of any preceding item, further comprising applying arelease coating to the modified microstructured surface on the modifiedmolding tool.

Item 10. The method of any preceding item, further comprisingreplicating a microstructured article having a microstructured surfacecomplementary to the pattern of the matrix of first microstructuralfeatures and the at least one discontinuous region of secondmicrostructural features.Item 11. The method of any one of items 1 to 9, further comprisingreplicating a metallic tool from the modified molding tool.Item 12. An article having a first major surface comprising firstmicrostructural features within a matrix of second microstructuralfeatures, wherein the first microstructural features are discontinuous,wherein collectively the first and second microstructural features forma pattern visible at least when viewed normal to the first majorsurface, and wherein the first and second microstructural features areindependently selected from the group consisting of cones, diffractiongratings, lenticulars, segments of a sphere, pyramids, cylinders,fresnels, and prisms.Item 13. The article of item 12, wherein the first and secondmicrostructural features independently have a pitch in a range from 0.1micrometer to 1000 micrometers.Item 14. The article of item 13, wherein the first pitch is up to 90% ofthe second pitch.Item 15. The article of item 13, wherein the first pitch is up to 50% ofthe second pitch.Item 16. The article of any one of items 12 to 15, wherein the patternincludes at least one of alphanumerics, a first trademark indicia, or afirst copyrighted indicia.Item 17. The article of any one of items 12 to 16, wherein the first andsecond microstructural features independently comprise at least one of athermosetting material or a thermoplastic material.Item 18. The article of any one of items 12 to 17, wherein the patterncomprises regions having no microstructural features.Item 19. An article having a first major surface comprising firstmicrostructural features and second microstructural features arranged ina pattern visible at least when viewed normal to the first majorsurface, wherein the first and second microstructural features aredifferent relative to each other, and are selected from the groupconsisting of cones, diffraction gratings, lenticulars, segments of asphere, pyramids, cylinders, fresnels, and prisms.Item 20. The article of item 19, wherein the first and secondmicrostructural features independently have a pitch in a range from 0.1micrometer to 1000 micrometers.Item 21. The article of item 20, wherein the first pitch is up to 90% ofthe second pitch.Item 22. The article of item 20, wherein the first pitch is up to 50% ofthe second pitch.Item 23. The article of any one of items 19 to 22, wherein the patternincludes at least one of alphanumerics, a first trademark indicia, or afirst copyrighted indicia.Item 24. The article of any one of items 19 to 23, wherein the first andsecond microstructural features independently comprise at least one of athermosetting material or a thermoplastic material.Item 25. The article of any one of items 19 to 24, wherein the patterncomprises regions having no microstructural features.

Advantages and embodiments of this invention are further illustrated bythe following examples, but the particular materials and amounts thereofrecited in these examples, as well as other conditions and details,should not be construed to unduly limit this invention. All parts andpercentages are by weight unless otherwise indicated.

EXAMPLES Materials

ArUA Aromatic urethane acrylate obtained from Cytec Industries Inc.,Smyrna, GA, under the trade designation “EBECRYL 220” AUA Aliphaticurethane acrylate obtained from Cognis Corporation, Cincinnati, OH,under the trade designation “PHOTOMER 6210” BAED-1 A bisphenol-A epoxydiacrylate obtained from Cytec Industries Inc. under the tradedesignation “EBECRYL 3720” BAED-2 A bisphenol-A epoxy diacrylateobtained from Cytec Industries Inc., under the trade designation“EBECRYL 3701” D1173 A photoinitiator obtained from Ciba Additives,Houston, TX, under the trade designation “DAROCUR 1173” DEAEMADiethylaminoethyl methacrylate, obtained from BASF, Freeport, TX HDDA1,6-hexanediol diacrylate, obtained from Cytec Industries Inc. I1035 Astabilizer obtained from Ciba Additives under the trade designation“IRGANOX 1035” I819 A photoinitiator obtained from Ciba Additives underthe trade designation “IRGACURE 819” IBOA Isobornyl acrylate, obtainedfrom Cytec Industries Inc. PAU Polyester aliphatic urethane obtainedfrom Morton International Inc., Seabrook, NH, under the tradedesignation “PN-04” T405 A stabilizer obtained from Ciba Additives underthe trade designation “TINUVIN 405” TMPTA Trimethylolpropanetriacrylate, obtained from Cytec Industries Inc. TPO(2,4,6-trimethylbenzoyl) diphenylphosphine oxide, a photoinitiator,obtained from Sigma-Aldrich, St. Louis, MOPreparation of Composition 1

A first radiation-curable composition (Composition 1) was prepared bymixing 25 wt. % BAED-1, 12% DEAEMA, 38 wt. % TMPTA, 25 wt. % HDDA, 0.5part per hundred (pph) TPO, 0.2 pph I1035 and 0.5 pph T405 in a glassjar. About 100 grams of the composition were prepared.

Preparation of Composition 2

A second radiation-curable composition (Composition 2) was prepared bymixing 74.5 wt. % AUA, 24.5 wt. % HDDA, 1.0 wt. % D1173 and 0.5 pph TPOin a glass jar. About 100 grams of the composition were prepared.

Preparation of Composition 3

A third radiation-curable composition (Composition 3) was prepared bymixing 58.4 wt. % BAED-2, 20.3 wt. % IBOA, 20.3 wt. % ArUA, and 1 wt. %I819. About 100 grams of the composition were prepared.

Example 1

A patterned tool was prepared using the following procedure, and asgenerally indicated in FIGS. 1 to 4B. About 10 grams of Composition 3were poured onto the upper microstructured face of a heatedmicrostructured tool and then spread uniformly using a 250 polyethyleneterephthalate (PET) film as a doctor blade. The tool was a nickel platemeasuring about 25 cm by 30 cm and 760 micrometers in thickness. Thetool had a microstructured surface consisting of cube corner cavitiesmeasuring 43 micrometers in depth with a pitch of 86 micrometers. Thetool rested on a magnetic hotplate set at 66° C. After filling cavitiesof the tool with Composition 3 using the doctor blade, a holographicfilm (obtained from Spectratek Technologies, Inc., Los Angeles, Calif.,under the trade designation “PEBBLES—0.002 INCHES, PRINT TREATEDPOLYESTER, TRANSPARENT”) was laminated to the resin using an ink rollerto minimize the resin thickness. A mask was placed on top of theholographic film, and two sheets of grooved film (obtained from 3MCompany under the trade designation “BRIGHTNESS ENHANCEMENT FILM (BEF)II 90/50”) with the grooves crossed at 90 degrees were placed on themask with the grooves facing the mask to collimate light. A 6.4millimeter sheet of window glass was placed on the grooved film toensure intimate contact of the microstructured tool, resin, holographicfilm, mask, and sheets of grooved film. Radiation was transmitted thoughthe glass, grooved film, mask, and the holographic film using a bank offluorescent lights (obtained from Philips Lighting, Somerset, N.J.,under the trade designation “TL 20W/03”) positioned about 3 cm from thetool for 60 seconds. The glass, grooved film, mask, and holographic filmwere removed from the coated tool, and uncured resin was rinsed from thetool using ethanol, giving a patterned tool. After drying, the patternedtool was irradiated with a Fusion “V” UV lamp (obtained from FusionSystems, Rockville, Md.) set at 600 watt/2.5 cm (100% power setting)under a nitrogen atmosphere, to provide additional cure. The lamp waspositioned 5 cm above the glass plate. The conveyor belt operated at15.2 meters/min. The patterned tool was then plasma treated withtetramethylsilane using the following procedure to provide a releasecoating on the microstructured side of the patterned tool.

The release coating was applied by depositing a silicon containing filmby plasma deposition. The deposition was carried out in a commercialreactive ion etcher system (obtained from Plasmatherm, Kresson, N.J.,under the trade designation “PLASMATHERM MODEL 3032”) configured forreactive ion etching (RIE) with a 26-inch (66 cm) lower poweredelectrode and central gas pumping. The chamber was pumped by a rootsblower (obtained from Edwards Vacuum, Ltd., Tewksbury, Mass., under thetrade designation “EDWARDS MODEL EH1200”) backed by a dry mechanicalpump (obtained from Edwards Vacuum, Ltd. under the trade designation“EDWARDS MODEL iQDP80”). RF power was delivered by a 5 kW, 13.56 MHzsolid-state generator (“RFPP MODEL RF50S0”) through an impedancematching network. The system had a nominal base pressure of 5 mTorr. Theflow rates of the gases were controlled by flow controllers (obtainedfrom MKS Instruments, Andover, Mass.). Samples of the polymeric toolswere placed on the powered electrode of the batch plasma apparatus. Theplasma treatment was done in a series of treatment steps. The featureswere first treated with an oxygen plasma by flowing oxygen gas at a flowrate of 500 cm³/min and plasma power of 200 watts for 60 seconds. Afterthe oxygen plasma treatment, a silicon containing film was thendeposited by flowing tetramethylsilane (TMS) gas at a flow rate of 150standard cm³/min, plasma power of 200 watts for 120 seconds. After theplasma deposition was completed, the chamber was vented to atmosphereand the patterned tool having a release coating was removed andsubsequently used as the tool in the following procedure.

FIG. 8 is a digital photographic image of resulting patterned tool 800(M₁ was about 26 millimeters).

Example 2

A prismatic retroreflective article was prepared using the followingprocedure. About 10 grams of Composition 1 were poured on the uppermicrostructured surface of the patterned tool of Example 1 and thenspread uniformly using a 250 micrometer polyester terephthalate (PET)film as a doctor blade. The patterned tool rested on a magnetic hotplateset at 66° C. After filling cavities of the patterned tool withComposition 1 using the doctor blade, giving a coated tool, an overlayfilm (light transmissive support layer) was then laminated to the coatedtool using an ink roller. The overlay film was a clear 50 micrometer PETfilm coated with 75 micrometers of PAU. The polyurethane coated side ofthe overlay film was in contact with the coated tool. The assemblyconsisting of the coated tool and overlay film was then placed on aconveyor belt and passed under a Fusion “D” UV lamp (Fusion Systems) setat 600 watt/2.5 cm to cure the coated composition. The conveyor beltoperated at 15.2 meters/min. The composite of overlay film and curedcoating composition was then removed from the patterned tool and againpassed under a Fusion “D” UV lamp (Fusion Systems) set at 600 watt/2.5cm, with the microstructures facing the UV lamp set at 600 watt/2.5 cmto complete the curing of the prismatic article.

FIGS. 9A and 9B are digital photographic images 900 of the resultingprismatic article under ambient and retroreflective lighting conditions,respectively (M₂ and M₃ were each about 26 millimeters).

Example 3

A metalized prismatic article was prepared according to the followingprocedure. The prismatic article of Example 2 was vapor coated with 100angstroms of titanium, followed by being vapor coated with 1500angstroms of aluminum. FIGS. 10A and 10B are digital photographic images1000 of the resulting prismatic article of Example 3 under ambient andretroreflective lighting conditions, respectively (M₄ and M₅ were eachabout 26 millimeters).

Example 4

A patterned tool was prepared using the following procedure, and asgenerally indicated in FIGS. 1 to 4B. About 30 grams of Composition 3were poured onto the upper microstructured face of a heated metalmicrostructured tool and then spread uniformly using a 250 micrometerPET film as a doctor blade. The metal microstructured tool was a nickelelectroformed plate measuring about 25 cm by 30 cm and 760 micrometersin thickness. The metal microstructured tool had a microstructuredsurface consisting of 90 degree prismatic grooves measuring 175micrometers in depth with a pitch of 350 micrometers. The metalmicrostructured tool rested on a magnetic hotplate set at 66° C. Afterfilling cavities of the metal microstructured tool with Composition 3using the doctor blade, a plasma tetramethylsilane release treatedgrooved film tool (obtained from 3M Company under the trade designation“THIN BRIGHTNESS ENHANCING FILM II (90/24)”) was laminated to the resinusing an ink roller to minimize the resin thickness. The grooves of thegrooved film tool were oriented at about 45 degrees relative to theprismatic grooves of the metal microstructured tool. A mask having apattern that was the negative of the image in FIG. 11A was placed on topof the grooved film tool, and a 6.4 millimeter sheet of window glass wasplaced on the mask to ensure intimate contact of the metalmicrostructured tool, resin, grooved film tool, and mask. Radiation wastransmitted though the glass, mask, and the grooved film tool using abank of fluorescent lights (“TL 20W/03”) positioned about 3 cm from theresin for 60 seconds. The glass, mask, and grooved film tool wereremoved from the coated metal microstructured tool, and uncured resinwas rinsed from the tool using ethanol, giving a patterned tool. Afterdrying, the coated metal microstructured tool was irradiated with aFusion “V” UV lamp (Fusion Systems) set at 600 watt/2.5 cm (100% powersetting) to irradiate the coated composition under a nitrogenatmosphere. The lamp was positioned 5 cm above the coated metalmicrostructured tool. The conveyor belt operated at 15.2 meters/min. Thecoated metal microstructured tool was plasma treated with oxygen andtetramethylsilane to provide a chemical release coating on the tool,using the procedure described in Example 1.

Example 5

A patterned film was produced using the following procedure. About 30grams of Composition 2 were poured on the upper microstructured surfaceof the patterned tool of Example 4 and then spread uniformly using a 250micrometer polyester terephthalate (PET) film as a doctor blade. Thepatterned tool rested on a magnetic hotplate set at 66° C. After fillingcavities of the patterned tool with Composition 2 using the doctorblade, giving a coated tool. An overlay film (light transmissive supportlayer) was then laminated to the coated tool using an ink roller. Theoverlay film was a clear, a clear 10 mil polycarbonate film waslaminated to the upper face of the coated tool using an ink roller. Theassembly consisting of the coated tool and overlay film was then placedon a conveyor belt and passed under a Fusion “D” UV lamp (FusionSystems) set at 600 watt/2.5 cm to cure the coated composition, forminga patterned film. The conveyor belt operated at 9.1 meters/min. Thepatterned film was then removed from the patterned tool, and againpassed under a Fusion “D” UV lamp (Fusion Systems) set at 600 watt/2.5cm, with the microstructures facing the UV lamp set at 600 watt/2.5 cmto complete the curing of the patterned film. FIG. 11A is a digitalphotographic image 1100 including elements 1110 and 1120 of theresulting patterned film, and FIGS. 11B and 11C are images of theresulting patterned film under 100× and 200× magnification, respectively(M₆ was about 26 millimeters, M₇ and M₈ were each about 350 micrometers,and the finer grooves in FIGS. 11B and 11C had a 24 micrometer pitch).

By directing a laser beam from a red laser pointer through the prismside of the composite film, diffraction patterns were produced andphotographed. FIG. 12A shows the laser diffraction pattern of the laserbeam passing through the larger grooves, and FIG. 12B shows thecombination diffraction pattern of the laser beam passing through boththe larger and the smaller grooves.

Example 6

A composite microlens array film was prepared by coating Composition 2between 50 micrometer PET film (obtained from DUPONT-TEIJIN, Chester,Va., under the trade designation “DUPONT-TEIJIN #618”) and a rotary toolat 49 deg C. generating microlenses (lens diameter=40 micrometers,radius of curvature=18.7 microns), according to the process described inU.S. Pat. No. 5,691,846 (incorporated herein by reference). The rubbernip roll gap was set to minimize the amount of resin over the cavitiesof the tool. The resin was cured through the PET with using two Fusion“D” UV lamps (Fusion Systems) set at 600 watt/2.5 cm (100% powersetting). The PET film was fed through the curing station at a rate of24.4 meter per minute. A release coating was applied to the lens surfaceof the microlens array film using the plasma deposition proceduredescribed in Example 1. After the plasma deposition procedure wascompleted, the chamber was vented to atmosphere and the compositemicrolens array film having a release coating was removed andsubsequently used as a “second molding tool” in the preparation of amolding tool of the present disclosure.

A molding tool of the present disclosure was prepared using thefollowing procedure, and as generally indicated in FIGS. 1 to 4B. About10 grams of Composition 3 were poured onto the microstructured surfaceof a first molding tool and then spread uniformly using a 250 micrometerPET film as a doctor blade. The first molding tool was a nickel platemeasuring about 25 cm by 30 cm and 760 micrometers in thickness. Thefirst molding tool had a microstructured surface having cube cornersmeasuring 43 micrometers in height with a pitch of 86 micrometers. Thefirst molding tool rested on a magnetic hotplate set at 66° C. Afterfilling cavities of the first molding tool with Composition 3 using thedoctor blade, the composite microlens array film having a releasecoating (i.e., the “second molding tool” as described above) waslaminated to the resin using an ink roller to minimize the resinthickness. A mask having a negative image of the pattern in FIG. 12A wasplaced on top of the composite microlens array film, and two sheets ofgrooved film (obtained from 3M Company under the trade designation“BRIGHTNESS ENHANCEMENT FILM (BEF) II 90/50”) with the grooves crossedat 90 degrees were placed on the mask with the grooves facing the maskto collimate light. A 6.4 millimeter sheet of window glass was placed onthe grooved film to ensure intimate contact of the microstructured tool,resin, microlens array film, mask, and sheets of grooved film. Radiationwas transmitted though the glass, grooved film, mask, and the compositemicrolens array film using a bank of fluorescent lights (obtained fromPhilips Lighting, Somerset, N.J., under the trade designation “TL20W/03”) positioned about 3 cm from the tool for 60 seconds. The glass,grooved film, mask, and composite microlens array film were removed fromthe coated tool, and uncured resin was rinsed from the coated tool usingethanol, giving a patterned tool. From this patterned tool, a nickelelectroformed replicate of the inverse topography was prepared as amolding tool. FIG. 13A is a digital photographic image 1300 of theresulting molding tool under ambient lighting conditions (M₉ is about 38millimeters). FIGS. 13B and 13C are magnified (400×) digitalphotographic images of regions of the resulting molding tool, showing anarea with microlenses 1331 in proximity to cube corners 1332 (FIG. 13B),and an area with microlenses and no cube corners (FIG. 13C).

Example 7

A retroreflective article was prepared using the following procedure.About 10 grams of Composition 2 were poured onto the uppermicrostructured face of the patterned microstructured tool of Example 6and then spread uniformly using a 250 micrometer PET film as a doctorblade. The tool rested on a magnetic hotplate set at 60° C. Afterfilling cavities of the tool with Composition 2 using the doctor blade,a clear 200 micrometer polycarbonate (PC) (obtained from SABICInnovative Plastics, Pittsfield, Mass., under the trade designation“LEXAN”) film was laminated to the upper face of the coated tool usingan ink roller. A masking film was then placed on top of the PC film. Themasking film was a 100 micrometer PET photolithographic printed filmhaving clear crescent-shaped images on a black field, which was thenegative of the images shown in FIG. 14, having field 1433 and crescents1434. A 0.6 cm thick clear glass plate was then placed on top of themask.

The assembly consisting of the coated tool, PC overlay film, maskingfilm and glass plate was then placed on a conveyor belt and passed underan ultraviolet (UV) lamp to cure the coated composition. In a firstcuring step, a Fusion “D” UV lamp (Fusion Systems) set at 600 watt/2.5cm (100% power setting) was used to irradiate the coated composition.The lamp was positioned 5 cm above the glass plate. The conveyor beltoperated at 10.7 meters/min. Following the UV exposure, the glass plateand masking film were removed from the coated tool. The assemblyconsisting of the coated tool and PC overlay film was then placed on aconveyor belt and passed under a Fusion “D” UV lamp (Fusion Systems) setat 600 watt/2.5 cm (100% power setting) to cure the coated composition.FIG. 14 is a digital photographic image of the resulting molding toolunder retroreflective lighting conditions (M₁₀ is about 38 millimeters,and M₁₁ is about 26 millimeters). Darker region 1431 includesmicrolenses (and the regions have little or no retroreflectivity), andlighter regions 1432, 1433 and 1434 include retroreflective cubecorners. Crescents 1434 received more irradiation than surrounding field1433, and in FIG. 13 crescents 1434 appear lighter than surroundingfield 1433.

Example 8

A retroreflective article was prepared using the procedure of Example 7,except that the masking film was not included. FIG. 15A is a digitalphotographic image of the resulting molding tool 1500 under ambientlighting conditions (M₁₂ is about 38 millimeters), and FIG. 15B is adigital photographic image of the resulting molding tool 1500 underretroreflective lighting conditions. In FIG. 15B, darker region 1531includes microlenses (and the regions have little or noretroreflectivity), and lighter regions 1532 and 1533 includeretroreflective cube corners.

Foreseeable modifications and alterations of this disclosure will beapparent to those skilled in the art without departing from the scopeand spirit of this invention. This invention should not be restricted tothe embodiments that are set forth in this application for illustrativepurposes.

What is claimed is:
 1. An article having a first major surfacecomprising: a plurality of regions of first microstructural featureswithin a matrix of second microstructural cavities formed on amicrostructured surface of a molding tool, the plurality of regions offirst microstructural features each comprising a first side comprising aplurality of first microstructural cavities, and a second side oppositethe first side, the second side comprising microstructural featurescomplementary to the second microstructural cavities on themicrostructured surface of the molding tool, wherein the matrix ofsecond microstructural cavities are interspersed with the plurality ofregions of first microstructural features such that the plurality ofregions of first microstructural features are discontinuous, whereincollectively the first and second microstructural cavities form apattern visible at least when viewed normal to the first major surface,and wherein the first and second microstructural cavities areindependently selected from the group consisting of cones, diffractiongratings, lenticulars, segments of a sphere, pyramids, cylinders,fresnels, and prisms.
 2. The article of claim 1, wherein the patternincludes at least one of alphanumerics, a first trademark indicia, or afirst copyrighted indicia.
 3. The article of claim 1, wherein theplurality of regions of first microstructural features and themicrostructured surface of the molding tool independently comprise atleast one of a thermosetting material or a thermoplastic material. 4.The article of claim 1, wherein the pattern comprises regions having nomicrostructural features.
 5. The article of claim 1, wherein the firstpitch is no more than 20% of the second pitch.
 6. The article of claim1, wherein the first pitch is no more than 10% of the second pitch. 7.The article of claim 1, wherein the first microstructural featurescomprise a cured resin.
 8. The article of claim 1, wherein the first andsecond microstructural cavities independently have a pitch in a rangefrom 0.1 micrometer to 1000 micrometers, wherein a first pitch of thefirst microstructural cavities is up to 50% of a second pitch of thesecond microstructural cavities.
 9. An article having a first majorsurface comprising: a plurality of regions of first microstructuralfeatures and a matrix of second microstructural cavities arranged in apattern visible at least when viewed normal to the first major surface,the plurality of regions of first microstructural features eachcomprising a first side comprising a plurality of first microstructuralcavities, and a second side opposite the first side, the second sidecomprising microstructural features complementary to the secondmicrostructural cavities on the microstructured surface of the moldingtool, wherein the plurality of regions of first microstructural featuresare within the matrix of the second microstructural cavities formed on amicrostructured surface of a molding tool, wherein the matrix of secondmicrostructural cavities are interspersed with the plurality of regionsof first microstructural features such that the plurality of regions offirst microstructural features are discontinuous, and wherein the firstand second microstructural cavities are different relative to eachother, and are selected from the group consisting of cones, diffractiongratings, lenticulars, segments of a sphere, pyramids, cylinders,fresnels, and prisms.
 10. The article of claim 9, wherein the patternincludes at least one of alphanumerics, a first trademark indicia, or afirst copyrighted indicia.
 11. The article of claim 9, wherein theplurality of regions of first microstructural features and themicrostructured surface of the molding tool independently comprise atleast one of a thermosetting material or a thermoplastic material. 12.The article of claim 9, wherein the pattern comprises regions having nomicrostructural features.
 13. The article of claim 9, wherein the firstpitch is no more than 20% of the second pitch.
 14. The article of claim9, wherein the first pitch is no more than 10% of the second pitch. 15.The article of claim 9, wherein the first microstructural featurescomprise a cured resin.
 16. The article of claim 9, wherein the firstand second microstructural cavities independently have a pitch in arange from 0.1 micrometer to 1000 micrometers, wherein a first pitch ofthe first microstructural cavities is up to 50% of a second pitch of thesecond microstructural cavities.